The present invention relates to laser beam scan type barcode readers which drive a scanning mirror to irradiate a barcode with a laser beam, receives a laser beam reflected by the barcode and reads the barcode.
As shown in FIG. 29, a conventional laser beam scan type barcode reader includes a laser beam scan type barcode scanner unit 1 and an analysis system 2 which receives a barcode image transferred from the scanner unit 1, analyzes it and stores resulting barcode data. As shown, the analysis system 2 includes a scanner unit power supply controller 2-1, a laser beam on/off controller 2-2, a timing signal both-edge determiner 2-3, an image signal both-edge determiner 2-4, an interrupt controller 2-5, a counter 2-6, a DMA controller 2-7, a work memory 2-8, a program memory 2-9, and a CPU 2-10.
Referring to FIGS. 29-32, a whole structure of the scanner unit 1 and the analysis system 2 and their operations will be described briefly. FIG. 30 is a whole schematic of the scanner unit 1. When a power supply is turned on in the system 2, a power supply on/off signal is applied from the scanner unit power supply controller 2-1 to a power supply 1-1 of the scanner unit 1 such that drive voltages are applied to a laser beam irradiation controller 1-2, a scanning mirror controller 1-3, a scan timing detector 1-4, a received beam analyzer 1-5, and a laser beam receiver 1-6 of the scanner unit to operate them. When a laser beam irradiation on/off signal is applied from the laser beam on/off controller 2-2 of the analysis system 2 to the laser beam irradiation controller 1-2, the laser beam irradiation controller 1-2 drives the laser beam irradiator 1-7 to cause same to start laser beam irradiation. At that time, the laser beam scanning mirror (vibration mirror or polygon mirror) 8 is driven by the scanning mirror controller 1-3 to reflect a laser beam from the laser beam irradiator 1-7 to scan a target barcode.
When the laser beam scanning starts in this way, the laser beam receiver 1-6 receives a reflected beam and transduces it to an electric signal. The received beam analyzer 1-5 converts a monochromatic image of the barcode to binary digital data depending on the scanning velocity, and transfers it as a barcode image signal to the image signal both-edge determiner 2-4. At this time, the scan timing detector 14 detects a particular position of the scanning mirror and delivers a pulse or an inverted pulse digital signal as a scan timing signal to the timing signal both-edge determiner 2-3.
FIG. 31 is a basic timing chart in which a high laser beam signal is output during a period between power supply on and off. The scanner unit 1 outputs a scan timing signal inverted each time one scan is completed, delivers the signal to the timing signal both-edge determiner 2-3, and a barcode image signal output for each scan to the image signal both-edge determiner 2-4. The timing signal both-edge determiner 2-3 detects a rise and a fall in the scan timing signal, and delivers one-scan complete information as an interrupt request to the interrupt controller 2-5, which ignores a stability wait state or an interrupt request occurring during an unfixed scan period of FIG. 31. When CPU 2-10 receives an interrupt request immediately after the scan operation is stabilized, it performs a decoding process which includes decoding barcode information transferred to the work memory 2-8 in accordance with a program stored in the program memory 2-9. The reading and transfer of the barcode to the work memory 2-8 is performed as follows. Each time a barcode image signal changes, immediately after the scan operation is stabilized, the image signal both-edge determiner 2-4 detects a change in the barcode image signal, delivers barcode image change information to the DMA controller 2-7, which gets data in the counter 2-6 and transfers it to the work memory 2-8. The counter 2-6 invariably performs a counting operation during the operation of the scanner unit 1. When the counter 2-6 receives from the DMA controller 2-7 a signal indicative of the completion of the DMA transfer, the counter 2-6 is cleared, and the counter performs a counting operation until a change in a next barcode image signal is detected.
Since the laser beam irradiation on/of signal is on between the power supply being on and off in the laser beam scan type barcode reader, the laser beam irradiation is performed invariably during the time, and the scan range of the laser beam scan mirror 1-8 becomes a laser beam irradiation range. Conventional techniques for control of the laser beam irradiation range (scan span) are as follows: when the laser beam scan mirror 1-8 is of a mirror vibration type, (1) a system for controlling a mirror amplitude, (2) a system for controlling an emission port diameter of the scanner unit, (3) a system for controlling a curvature of the mirror obtained when the mirror is curved, and (4) a system for controlling the laser beam irradiation range by a refractive index of a medium which refracts the laser beam. When the laser beam scan mirror 1-8 is a polygon mirror, there is a system for changing the number of polygon mirrors in addition to the above mentioned systems (2)-(4).
The mirror amplitude controlling system (1) is possible in principle. However, in order to reduce the scan span, safety is required to be considered because the laser beam irradiation is performed even in a scan stop state where the vibration direction changes. More specifically, as shown in FIG. 14, right and left scans are performed alternately and repeatedly by the vibration mirror. When the scan direction changes, the mirror velocity temporarily becomes zero in both the right and left scans. Thus, the laser beam is shielded by the system housing so as not to leak out to the outside when the scan direction changes, in consideration of safety. In this case, as shown in FIG. 32, the effective irradiated beam quantity in the readable scanning range is about 70% of the whole irradiation beam quantity, and a laser beam quantity of about 30% is shielded, which leads to useless power consumption.
The irradiation port diameter controlling system (2) requires a physical or optical shutter device. Since the curvature controlling system (3) requires a function of deforming the flexible mirror physically in a state where the mirror is moving, its mechanism and circuit become large-scaled and there are difficulties in its installation space and power consumption. The laser beam refractive index controlling system (4) changes the refractive index, for example, of a liquid crystal device, and requires the liquid crystal device. Since the polygon mirror number changing system (5) is required to prepare for many polygon mirrors such as triangular, pentagonal, . . . mirrors and a switchingly selecting device for them, it has drawbacks similar to those in the systems (2) and (3). As described above, in any of the systems (1)-(5), some device is required to be added or the devices which basically compose the scanner unit are required to be changed greatly, which is a big hindrance to reducing the size and power consumption of the whole system.
It is therefore an object of the present invention to provide a laser beam scan type barcode reader which reads at least a pair of marks which correct the start and stop positions of laser beam irradiation, and corrects an actual scan span in which the laser beam is turned on in one scan period, based on the start and stop positions of the laser beam irradiation determined by the at least one pair of marks to thereby securely prevent structural, functional, and characteristic deviations of the scanner unit from the standards from influencing the scan span of the laser beam.
According to the present invention, there is provided a laser beam scan type barcode reader which drives a scan mirror to irradiate a laser beam against a barcode, receives a reflected beam from the barcode, and reads the barcode, comprising:
barcode reading means for driving a scan mirror to irradiate a laser beam on a selected one of a barcode and a pair of spaced marks, for receiving a reflected beam from the selected one of the barcode and the pair of marks, and for reading the selected one of the barcode and pair of marks;
detecting means, responsive to the barcode reading means reading the pair of marks, for detecting the start and stop positions of the laser beam irradiation determined by the pair of marks;
setting means for setting therein as scan span control information the start and stop positions detected by the detecting means; and
laser beam irradiation driving means for controlling the turning on/off of the laser beam in one scan period based on the start and stop positions set as the scan span control information in reading the barcode to thereby control the actual scan span in which the laser beam is on in the one scan period based on the start and stop positions of the laser beam irradiation determined by the pair of marks.